Add support for latest Rust features via `--features latest_rust`

Cargo.toml

@@ -11,6 +11,9 @@ documentation = "https://docs.rs/electrs/"
 readme = "README.md"
 edition = "2018"
 
+[features]
+latest_rust = []  # use latest Rust features (otherwise, support Rust 1.32)
+
 [dependencies]
 arrayref = "0.3"
 base64 = "0.10"

src/daemon.rs

@@ -13,7 +13,9 @@ use std::collections::{HashMap, HashSet};
 use std::io::{BufRead, BufReader, Lines, Write};
 use std::net::{SocketAddr, TcpStream};
 use std::path::PathBuf;
-use std::sync::{Arc, Mutex, atomic::{AtomicU64, Ordering}};
+#[cfg(feature = "latest_rust")]
+use std::sync::atomic::{AtomicU64, Ordering};
+use std::sync::{Arc, Mutex};
 use std::time::Duration;
 
 use crate::errors::*;
@@ -266,15 +268,15 @@ impl Connection {
     }
 }
 
+#[cfg(feature = "latest_rust")]
 struct Counter {
     value: AtomicU64,
 }
 
+#[cfg(feature = "latest_rust")]
 impl Counter {
     fn new() -> Self {
-        Counter {
-            value: 0.into(),
-        }
+        Counter { value: 0.into() }
     }
 
     fn next(&self) -> u64 {
@@ -283,6 +285,26 @@ impl Counter {
     }
 }
 
+#[cfg(not(feature = "latest_rust"))]
+struct Counter {
+    value: Mutex<u64>,
+}
+
+#[cfg(not(feature = "latest_rust"))]
+impl Counter {
+    fn new() -> Self {
+        Counter {
+            value: Mutex::new(0),
+        }
+    }
+
+    fn next(&self) -> u64 {
+        let mut value = self.value.lock().unwrap();
+        *value += 1;
+        *value
+    }
+}
+
 pub struct Daemon {
     daemon_dir: PathBuf,
     network: Network,